SU-E-T-23: TomoTherapy Patient QA Using Exit Detector Measurement of Pre-Treatment In-Air Delivery

Area of Science:

• Medical Physics
• Radiation Oncology
• Quality Assurance

Background:

• Current TomoTherapy patient-specific QA relies on time-consuming phantom setups with ion chambers and film.
• Phantom setup errors can compromise the accuracy of traditional QA procedures.
• A more efficient and reliable QA method is needed for TomoTherapy workflows.

Purpose of the Study:

• To explore the feasibility of using TomoTherapy's intrinsic exit detectors for patient-specific QA.
• To develop and validate a method for measuring fluence using exit detectors during pre-treatment in-air delivery.
• To assess the efficiency and accuracy of this novel QA approach for the STAT-RAD workflow.

Main Methods:

• Patient plans were converted to calibration procedures with the couch retracted.
• In-house software reconstructed exit detector signals from DICOM data using leaf and tongue-and-groove profiles.
• An algorithm estimated point dose differences by comparing reconstructed and measured detector signals.
• The method was tested on patient plans, with introduced errors to validate against ion chamber measurements.

Main Results:

• The in-house software accurately reconstructed exit detector signals with <1% error.
• The estimated point dose agreed within 3% of ion chamber measurements.
• The in-air delivery QA method proved effective in detecting introduced errors.

Conclusions:

• Using TomoTherapy's exit detectors for patient-specific QA is feasible and efficient.
• This novel approach is faster and simpler than conventional QA methods.
• The exit detector method offers a reliable alternative for ensuring treatment accuracy.